A light emitting diode (LED) can directly convert electric energy into light energy. An LED chip includes a P-type semiconductor in which holes dominate and an N-type semiconductor in which electrons dominate. A “P-N junction” is formed between the P-type semiconductor and the N-type semiconductor when the two semiconductors are connected. The principle of light emission of the LED is that when a current is applied to the chip via a conductive wire, the electrons are pushed to the P-type region and are recombined with the holes in the P-type region, such that energy is emitted in a form of photons. The LED, as a new light source, has been widely used in the lighting field due to its feature of energy saving, environmental protection and a long life. The Nichia Chemical in Japan has patent applications for a blue-light LED with a substrate made of sapphire, application numbers of which are JP19960198585, 19960244339, JP19960245381, JP19960359004 and JP19970081010. The LED chip with a sapphire substrate emits light in a solid angle of 360 degrees, and a current LED packaging light source is a single-side light source, which requires a reflective substrate reflecting lights emitted from a back side and a lateral side of the LED chip, such that the reflected lights are emitted from a front surface. In this case, a large portion of the lights is absorbed by a material due to multiple reflections, thereby reducing overall luminous flux of the LED packaging light source and limiting improvement of light effect of the LED light source.
Therefore, a LED light emitting device which emits lights from two sides is provided. With reference to FIGS. 1A to 1E, a main fabrication idea of the LED light emitting device is described as follows.
A transparent base 10 is provided. Multiple columns of LED chips are arranged on the transparent base 10 by a die bonding process and multiple LED chips 11 are arranged on each column. By a wire-bonding process, in a same column, a pad of a positive electrode on a surface of an LED chip is connected to a pad of a negative electrode on a surface of an LED chip adjacent to the LED chip via a conductive wire 12. The whole transparent base 10 is placed into a mould 15. A mixture 14 including a fluorescent powder and a packaging adhesive is attached on a front surface and a back surface of the transparent surface 10 by a molding process. The multiple columns of LED chips are cut into light bars 16 each including one column of LED chips.
In the LED light bar fabricated by the above method, since the transparent base is used in conjunction with the LED chip having a transparent substrate, a front surface and a back surface of the light bar each can emit lights, thereby improving a light utilization efficiency of the LED.
However, the LED light bar has the following two problems.
Since the packaging adhesive covers the front surface and the back surface of the transparent base, after the transparent base is cut into the LED light bars, lateral surfaces of the LED light bar can not be covered by the packaging adhesive. In this case, lights leak from the lateral surfaces of the LED light bar, thereby affecting overall uniformity of light emitting of the LED light bar.
In addition, based on the above problem, LED manufacturers always increase the amount of fluorescent powder to reduce a color temperature at a position where the LED bar leaks lights, to meet a customer's requirement for a color temperature of the whole LED light bar. Taking a blue-light LED chip as an example, since a color temperature of blue lights leaking from the lateral surfaces is much greater than a color temperature of lights emitted from the front and back surfaces, the overall color temperature of the LED light bar is increased. Therefore, in order to reduce the color temperature of the LED light bar, the manufacturers have to use more fluorescent powder in the LED light bar, which increases the cost, and affects a light emitting effect of the front and back surfaces of the LED light bar.
Therefore, in the industry, the lateral-surface light leakage of the LED light bar is an urgent problem to be solved.